Inkjet printing mechanisms use cartridges, often called “pens,” which eject drops of ink onto a page. Each pen has a print head formed with very small nozzles through which the ink drops are fired. Drum-type ink jet printing systems generally include one or more print heads disposed over a rotating cylindrical drum. The print media is carried by the rotating drum past the print heads, which eject drops of ink in a desired pattern upon the media.
In order to maintain good image quality, proper maintenance of the condition of the print heads is desirable. An improperly maintained print head can become clogged and/or become the source of dot placement errors that reduce print quality. To that end, inkjet printing devices also typically include a print head service station, generally located outside the print zone, to allow cleaning and protection of the print heads. Print head service stations usually include a waste ink collector, called a “spittoon”, into which a number of drops of ink are periodically ejected, or “spit”, from each nozzle to flush out drying ink. If spitting is not performed, the first few drops ejected from each nozzle can have poor trajectory or be of low optical density, resulting in visible image or print quality defects.
In many printing systems, the print head assembly moves from the print zone to the service station for print head servicing during non-printing periods and during the shutdown process. However, speed is a desirable printing consideration. Moving the print heads from the print zone (above the drum) to a service station that is off the drum, and then back again is a relatively slow process, which increases downtime and reduces throughput of the printing system. Additionally, moving the print heads to a service station outside the print zone can introduce print head position errors, which can harm print quality.